1. Field of the Invention
This invention generally relates to a scanning arrangement in a scanner operative for repetitively scanning indicia having parts of different light reflectivity, for example, bar code symbols, and, more particularly, to operating such a scanning arrangement at high speeds in single or multi-axis scan patterns.
2. Description of the Related Art
Various optical readers and optical scanners have been developed heretofore to optically read bar code symbols applied to objects in order to identify the object by optically reading the symbol thereon. The bar code symbol itself is a coded pattern comprised of a series of bars of various widths and spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting properties. The readers and scanners electro-optically decoded the coded patterns to multiple digit representations descriptive of the objects. Scanners of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,808,804; 4,816,661; 4,816,660; and 4,871,904, all of said patents having been assigned to the same assignee as the instant invention and being hereby incorporated herein by reference.
As disclosed in the above-identified patents and applications, a particularly advantageous embodiment of such a scanner resided, inter alia, in emitting a light beam, preferably a laser beam, emitted from a light source, preferably a gas laser or a laser diode, and in directing the laser beam to a symbol to be read. En route to the symbol, the laser beam was directed to, and reflected off, a light reflector of a scanning component. The scanning component moved the reflector in a cyclical fashion and caused the laser beam to repetitively scan the symbol. The symbol reflected the laser beam incident thereon. A portion of the incident light reflected off the symbol was collected and detected by a detector component, e.g. a photodiode, of the scanner. The photodiode had a field of view, and the detected light over the field of view was decoded by electrical decode circuitry into data descriptive of the symbol for subsequent processing. The cyclically movable reflector swept the laser beam across the symbol and/or swept the field of view during scanning.
U.S. Pat. Nos. 4,387,297 and 4,496,831 disclose a high-speed scanning component including an electric motor operative for reciprocatingly oscillating a reflector in opposite circumferential directions relative to an output shaft of the motor. Electrical power is continuously applied to the motor during scanning. The light beam which impinges on the light reflector is rapidly swept across a symbol to b e scanned in a predetermined cyclical manner. The scanning component comprises at least one scan means for sweeping t he symbol along a predetermined direction (X-axis) lengthwise thereof. The scanning component may also comprise another scan means for sweeping the symbol along a transverse direction (Y-axis) w which is substantially orthogonal to the predetermined direction, to thereby generate a raster-type scan pattern over the symbol. In addition to a single scan line and the raster-type pattern, other types of scan patterns are also possible, such h as, x-shaped, Lissajous, curvilinear (see U.S. Pat. No. 4,871,904), etc. For example, if the X and Y axis scanning motors are both driven such that the light reflectors are driven at a sinusoidally-varying rate of speed, then the scan pattern at the reference plane will be a Lissajous-type pattern for omni-directional scanning of the symbols. The use of two separate scanning motors and control means to produce the multi-axis and omni-directional scanning pattern increases material and labor costs as well as the amount of electrical power needed to operate the scanner. In addition, the relatively complicated motor shaft and bearing arrangements of the scanning components may result in a useful life that is inadequate for some applications. Furthermore, the scanning components disclosed in U.S. Pat. Nos. 4,387,297 and 4,496,831 are designed for miniature light reflectors and are not well suited for large scale reflectors.
It is a general object of this invention to advance the state of the art of scanners for reading indicia of different light reflectivity, particularly laser scanners for reading bar code symbols.
An additional object of this invention is to provide novel high-speed scanning elements and novel scanning methods of operation.
Yet another object of this invention is to conveniently generate single line, multi-line or omni-directional scan patterns with the same scanning elements.
A further object of this invention is to provide a scanning arrangement having an increased scan line amplitude.
It is another object of this invention to minimize the number of elements comprising the scanning component.
Another object of this invention is to increase the working lifetime of the scanning components.
In keeping with these objects, and others which will become apparent hereinafter, this invention resides, briefly stated, in an arrangement for, and a method of, scanning indicia having parts of different light reflectivity by directing light toward the indicia and by collecting reflected light returning from the indicia. This invention comprises a scanner component supported by holder means for angular oscillating movement in a single scan direction between a pair of scan end positions or alternatively, in first and second scan directions between first and second pairs of scan end positions. According to this invention, read-start means are provided for moving the component between the scan end positions.
In one feature, the component is simultaneously angularly oscillated between the first and second pair of scan end positions for directing light along the first and second scan directions to thereby effect a multi-directional scan pattern over the indicia.
In one embodiment, the holder means is a planar leaf spring having opposite ends anchored and the scanner component mounted on a bent central portion of the spring. The read start means is comprised of a permanent magnet mounted to the holder and an electromagnetic coil for displacing the magnet in response to a driving signal. By energizing the-nearby coil, the magnet and, in turn, the scanner component are oscillated, preferably at the resonant frequency of the component/magnet assembly.
In another embodiment, the holder means is a tuning fork having a permanent magnet fixedly mounted on one arm of the fork and the scanner component fixedly mounted on the other arm. The read-start means is comprised of a n electromagnetic coil for displacing the magnet and, in turn, for oscillating the scanner component in a scan which extends in the first direction over the indicia. The stem of the fork may also be oscillated by a second read-start means comprised of a stepper motor to scan the indicia in the second direction generally perpendicular to the first direction to effect two-dimesional scanning.
In a further embodiment of the present invention, a two-dimensional scan pattern over the indicia is advantageously effected by a holder means that is constructed for mounting the component for angular oscillating movement along first and second axes in response to a single read-start means.
In one embodiment, the first and second vibratory means are mounted in orthogonal planes relative to each other and cooperate for angular oscillatory movement of the component about the first and second axes. The first vibratory means is constructed to vibrate at a high range of frequencies and the second vibratory means is constructed to vibrate at a low range of frequencies in response to a driving signal. The driving signal is comprised of a superposition of a first A.C. signal within the high frequency range and a second A.C. signal within the low frequency range to thereby effect a two-axis raster-type scan pattern. In this embodiment, the first vibratory means is a generally U-shaped leaf spring having a permanent magnet mounted on one arm and the scanner component mounted on the other arm, and the second vibratory means is a generally planar leaf spring having one end secured to the arm of the U-shaped spring having the magnet and the other end secured to a base forming a vibration pivot line. The superimposed driving signal is supplied to an electromagnetic coil for displacing the magnet and, in turn, for oscillating the scanner component in two orthogonal scan directions over the indicia to form the raster pattern. In an alternative embodiment, the second vibratory means includes a generally S-shaped leaf spring secured to the planar leaf spring.
In another embodiment of a two-axis raster-type scan arrangement, the holder means includes a generally planar leaf spring having one end secured to a base to form a vibration pivot line and the component mounted on the free end of the spring. The center of mass of the component is offset from the axis formed by an electromagnetic coil and a magnet mounted to the leaf spring. The offset center of mass of the component provides a restoring force to torsionally vibrate the planar spring along the first scan direction at a high range of frequencies and the leaf spring vibrates about the pivot line along the second scan direction at a low range of frequencies to effect the raster-type scan pattern over the indicia in response to a superimposed high and low frequency driving signal.
In another feature of the invention, an omni-directional scan pattern over the indicia is provided. First and second vibratory means are arranged such that in response to a superposition of driving signals having a frequency ratio relative to each other of 5:1 or less, a Lissajous scan pattern is effected. The first vibratory means is a generally U-shaped leaf spring in which one arm is mounted to the component and the other arm is mounted to the second vibratory means which includes a generally planar leaf spring secured to the base forming a pivot line. The leaf spring includes a permanent magnet mounted on one side that cooperates with an electromagnetic coil. Mounted on the other side of the leaf spring is the U-shaped spring with the component. The direction of vibration of the leaf spring about the pivot line and the direction of vibration of the U-shaped spring are the same. In this embodiment, the weight of the U-shaped spring and component results in a torsional vibration of the planar spring for oscillating the component along one scan direction and the vibration of the leaf spring about the pivot point results in the component being oscillated along a second scan direction. The simultaneous vibration in the two axes generated by the 5 to 1 or less frequency superimposed driving signal provides the Lissajous scan pattern.
In an improved construction of the U-shaped spring comprising the holder means in the various embodiments described above, the angular amplitude of the scan line produced by the U-shaped spring is increased by providing the spring with asymmetrically dimensioned arms. The asymmetrically dimensioned construction may be implemented to increase the angular amplitude in either a one or two axis scan arrangement.
In a further feature of the present invention, various improvements in the means for providing the necessary restoring force to repeatably oscillate the compound between scan end positions is provided.
In one embodiment, the read-start means includes a magnetic return means that provides a spring-like restoring force for oscillating the component between scan end positions. The magnetic return means includes a stationary permeable magnetic core positioned adjacent a movable permanent magnet at an equilibrium position. The magnet is operatively connected to the component for moving the component between scan end positions. The permanent magnet is alternately attracted to and repelled from an electromagnetic coil when the coil is energized by an alternating current driving signal. During actuation of the coil, the magnet passes back and forth over the core which alternately magnetizes the core with a polarity opposite to the side of the magnet facing the core thereby creating a magnetic restoring force causing the magnet to return to the equilibrium position over the center of the core. In a further embodiment, a second electromagnetic coil may be provided in operative arrangement with the core to strengthen the magnetic field of the core. Alternatively, the core may be formed of a permanent magnet material.
In another feature of the invention, the restoring means may be in the form of an elastic member, such as a room temperature vulcanizer, attached to the component that acts like a spring to restore the component to the rest position.